Nabiz Rahpoe

Relative drifts and biases between six ozone limb satellite measurements from the last decade

Abstract. As part of European Space Agencys (ESA) climate change initiative, high vertical resolution ozone profiles from three instruments all aboard ESAs Envisat (GOMOS, MIPAS, SCIAMACHY) and ESAs third party missions (OSIRIS, SMR, ACE-FTS) are to be combined in order to create an essential climate variable data record for the last decade. A prerequisite before combining data is the examination of differences and drifts between the data sets. In this paper, we present a detailed analysis of ozone profile differences based on pairwise collocated measurements, including the evolution of the differences with time. Such a diagnosis is helpful to identify strengths and weaknesses of each data set that may vary in time and introduce uncertainties in long-term trend estimates. The analysis reveals that the relative drift between the sensors is not statistically significant for most pairs of instruments. The relative drift values can be used to estimate the added uncertainty in physical trends. The added drift uncertainty is estimated at about 3 % decade−1 (1σ). Larger differences and variability in the differences are found in the lowermost stratosphere (below 20 km) and in the mesosphere.

Impact of Short-Term Solar Variability on the Polar Summer Mesopause and Noctilucent Clouds

The Earth’s middle atmosphere is affected by short-term solar variability in a variety of ways. This chapter focuses on the investigation of two different short-term solar effects on the polar summer mesopause region and on noctilucent clouds (NLCs). First, the effect of solar proton events (SPEs) on the thermal conditions near the polar summer mesopause and consequently on NLCs is discussed. An analysis of the SBUV(/2) time series to identify examples of NLC depletion due to SPEs shows that NLCs are probably frequently affected during strong SPEs. As part of this study a physical mechanism explaining a dynamically induced warming at the polar summer mesopause during and after SPEs is investigated using model simulations with the Kuhlungsborn Mechanistic General Circulation Model (KMCM). A second aspect related to the effect of SPEs on NLCs is on the SPE-induced ion-chemical conversion of H2O to HO x , leading to a possible sublimation of NLCs. However, this effect was found to be of minor importance compared to the dynamically induced temperature effect. Second, we discuss the recently discovered 27-day solar cycle signature in NLCs, which was identified in SCIAMACHY as well as SBUV satellite observations of NLCs using cross correlation analysis and the superposed epoch method. NLC occurrence rate and albedo anomalies are anti-correlated with Lyman-α anomalies with a time-lag of 1 day at most. The sensitivities of the NLC albedo anomalies to Lyman-α forcing in terms of the 27-day and the 11-year solar cycle were found to agree within their uncertainties. This finding suggests that the same underlying physical mechanism drives the 27-day as well as the 11-year solar cycle signature in NLCs. The exact mechanism is still unknown, however.